1. Field of the Invention
The present invention relates to an ink composition, an ink cartridge, a nozzle plate, an ink jet head, and a recording apparatus, which are suitable for ink jet recording.
2. Description of the Background Art
Ink containing a colorant (a dye or a pigment), a humectant and water is well known in the art as ink for use in ink jet recording. However, an image that is formed on a recording medium such as recording paper by using ink containing a colorant has poor water-resistivity, i.e., when the image is wet with water, the colorant bleeds into the water. The water-resistivity will be very poor when the image is recorded on plain paper (a type of paper that is widely available on the market for with electrophotographic copiers, among others, but is not intended to have optimal structure, composition, properties, etc., for ink jet recording).
In view of this, it has been proposed in the art to improve the water-resistivity of an image on a recording medium by using ink containing a hydrolyzable silane compound (an organic silicon compound) (see, for example, Japanese Laid-Open Patent Publication Nos. 10-212439, 11-293167, 11-315231 and 2000-178494). With such ink, when the water (solvent) of an ink droplet attached to the recording medium evaporates or permeates into the recording medium, the silane compound remaining on the recording medium undergoes condensation polymerization, and the condensation-polymerized silane compound encloses the colorant. Therefore, even if the image on the recording medium is wet with water, the colorant does not bleed into the water. Thus, the water-resistivity of the image is improved.
An ink jet type recording apparatus includes a nozzle plate with nozzles formed therein, and ink is discharged through the nozzles and lands on the recording medium. If the nozzle plate is not sufficiently water-repellent around the nozzles, some ink is likely to be deposited on the nozzle plate around a nozzle. Then, the ink deposit deflects the discharge direction of the next ink droplet to be discharged, thereby lowering the image quality.
It is known in the art to form a water-repellent film on the ink exit side of a nozzle plate. For example, Japanese Laid-Open Patent Publication No. 6-8448 describes forming a polymerized fluoro-compound film on the surface of a nozzle plate. Moreover, for example, Japanese Laid-Open Patent Publication No. 9-164689 describes coating the surface of a nozzle plate with an electroless nickel plating film in which polytetrafluoroethylene fine grains are dispersed. Furthermore, Japanese Laid-Open Patent Publication No. 2000-280481 describes forming, on the surface of a nozzle plate, a sol-gel film containing a fluoroalkyl silane. In addition, Japanese Laid-Open Patent Publication No. 2001-63043 describes forming, on the surface of a nozzle plate, a water-repellent film by a high-frequency plasma CVD (chemical vapor deposition) method using an organic silicon compound as a material.
If a water-repellent film as described in these publications is formed on the surface of a nozzle plate 9, sufficient water repellency is obtained to prevent ink from being deposited on the nozzle plate 9, in a case where normal ink, i.e., ink that does not contain a hydrolyzable silane compound, is used.
However, as illustrated in FIG. 7, active hydrogen, such as a hydroxyl group, a carboxyl group or a silanol group, is present on the surface of the nozzle plate 9 (the surface of a water-repellent film 9a). Therefore, when ink that contains a hydrolyzable silane compound and has improved water-resistivity is used, the active hydrogen present on the surface of the nozzle plate 9 and the silane compound contained in the ink react with each other so that the silane compound (ink) is deposited on the surface of the nozzle plate 9. The silane compound contains an amino group for interaction with the colorant. Therefore, when the silane compound is deposited on the surface of the nozzle plate 9, the surface of the nozzle plate 9 is turned hydrophilic by the amino group. Then, the ink deposit on the nozzle plate 9 deflects the discharge direction of the next ink droplet to be discharged through a nozzle, thereby causing a shift in the ink landing position. Moreover, once some ink is deposited on the nozzle plate 9, the surface of the nozzle plate 9 is turned hydrophilic, thereby attracting more ink to be deposited thereon. As the amount of the ink deposit on the nozzle plate 9 increases, a nozzle 14 may possibly be clogged, thereby preventing subsequent ink droplets from being discharged from the nozzle 14.
A normal recording apparatus periodically performs a cleaning operation of wiping the ink deposit off the surface of the nozzle plate with a rubber-made blade, or the like. However, when ink containing a hydrolyzable silane compound is deposited on the nozzle plate, such a cleaning operation promotes the reaction between the active hydrogen on the surface of the nozzle plate and the silane compound. Therefore, the ink deposit cannot be wiped off the nozzle plate. Thus, when ink containing a hydrolyzable silane compound is used, the shift in the ink landing position and the nozzle clogging cannot be prevented by cleaning the nozzle plate.